Re: [PLUG] hubs vs switches

[Jeff Dean <jdean@ieee.org>]

A hub is an bridge with a bunch of ports.  That means that it forwards all 
traffic received on a port to all other ports.  When you extrapolate this 
to a large network with all the ports chattering to all the other ports, 
you can imagine that the hub gets pretty swamped.  In this case, it's not 
much different from a piece of coax, except that it's a "star" 
configuration with individual wiring to each host.

A switch (sometimes called a "switching hub" by marketeers) looks similar 
but works in a fundamentally different way.  Instead of bridging like a 
hub, a switch looks at the MAC address you're sending to and forwards your 
packets only to the port that includes that device.  For broadcasts and 
unknown destinations, it will forward just like a hub, but it remembers 
where answering devices are and stores that information in a table.  A 
switch does a lot of this learning when it first powers up.  The result is 
that each individual port is a private network between the switch and the 
host.  This private network is often called a "collision domain" because 
the only traffic on the wire comes from those two systems, and the 
likelihood of collisions is much lower than a shared network.

For switched Ethernet, you can get 10Mbps or 10Mbps solutions, and many 
switches do both.  The cost per port for 100Mbps is higher, and even today 
remains prohibitive for large installations.  Remember, web browsing and 
other administrative work may not warrant the costs of a 100Mbps 
infrastructure.  Also, older CAT3 cable won't handle 100Mbps anyway, so 
older wiring would need to be upgraded to take advantage of the faster switch.

I was lucky enough to inherit a hub-based 10Mbps production development 
network a few years ago.  Switching was still relatively expensive then, 
but we implemented a hybrid switched environment to reduce the problem 
until a better solution could be found.  Later, the entire corporate LAN 
was migrated to switched 10Mbps (all Cisco).  Now, despite the lack of 
100Mbps, none of the client ports sees any significant traffic.

I hope that helps.

jd

At 02:58 PM 3/20/01, you wrote:
> Hi all!
>
>         What is better a switch or a hub?  What is the difference?
>
> Does anyone know where to get a swtich?  We have a hub now... but I hear
> that switches are the latest greatest thingy
>
> Just wondering what they actually do... instead of what they are rumored to
> do.
>
> Does anyone have any sort of experience with this sort of thing?
>
> Thanks all
>
> Anthony
>
>
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Jeff Dean
jdean@ieee.org


______________________________________________________________________
Philadelphia Linux Users Group       -      http://www.phillylinux.org
Announcements-http://lists.phillylinux.org/mail/listinfo/plug-announce
General Discussion  -  http://lists.phillylinux.org/mail/listinfo/plug